By far case study answer biggest variety of tree types are dicotyledons; they are represented by such popular groups as birches, elms, hollies, magnolias, maples, oaks, poplars, ashes, and willows. The tree is not an immutable biological category however rather a human idea based upon visual criteria. This can be contrasted with a shrub, which might be loosely certain as a woody plant with dissimilar stems that is, most of case study answer times, less than 3 metres about 10 feet tall. However, a types fitting case study solution description of either in one area of case study answer world may not always do so in other regions, because a variety of tensions form case study answer routine of case study solution fully grown plant. For example, case study answer spruce and fir may flourish in case study solution tree form at case study answer base of a mountain but presume a shrub kind near case study solution mountaintop, case study answer variation due primarily to stresses exerted by such ecological circumstances as elevation, temperature level, and oxygen tension. As seen in case study solution part above, trees are found out among numerous plant households that likewise consist of shrubs and herbs, in order that case study answer idea of tree is not a phylogenetic one.